Carbon Capture & Storage 101 : More Terms to Know

As carbon reduction initiatives grow in importance, and as consumers and customers opt to do business with organizations who commit to decarbonization, companies across industries are developing long-term strategies to reduce their carbon emissions across their supply chain and operations. As you navigate through the ESG and carbon-reduction planning process, these definitions—our latest addition to our series on carbon capture and storage terms—define common terms and provide context for how they fit into the broader carbon emission and decarbonization discussion. 

Pre-Combustion Carbon Capture: Pre-combustion carbon capture involves removing CO2 from fossil fuels before they are combusted. This process typically occurs through a chemical reaction, which often produces a purer concentration of a desirable substance by removing more CO2. For instance, in a mixture of hydrogen, carbon monoxide, water vapor, CO2, and other gases, a chemical reaction would convert carbon monoxide and water to H2 and CO2. The resulting CO2 can then be captured and stored, and the mixture will now burn more cleanly thanks to the higher concentration of H2.

Post-Combustion Carbon Capture: Post-combustion carbon capture involves removing CO2 from produced gases after combustion through the use of chemical solvents. Flue gas streams at factories and plants are carbon-heavy, so an absorber is installed and holds a chemical solvent, which reacts selectively with carbon dioxide. As the gas passes through the absorber, the carbon dioxide reacts with the solvent and is absorbed into it, which purifies the flue gas streams exiting the plant.  

Oxy-Combustion Carbon Capture: Oxy-combustion carbon capture occurs when pure oxygen is used in combustion processes. Using pure oxygen instead of air for combustion results in a dramatic reduction in the volume of flue gas, which in turn reduces the volume of CO2 produced.  

Solid DAC: Solid direct air capture (DAC) removes CO2 from the atmosphere through chemical reaction. Similar to the scrubbers used in power plants, solid DAC relies on a solid chemical adsorbent. When air passes over the chemical adsorbent, a selective reaction occurs with the CO2 within the air, and it is then pulled and trapped in the adsorbent. 

Liquid DAC: Liquid direct air capture (DAC) is similar to solid DAC, except it relies on a liquid solvent to remove CO2 from the atmosphere. When air passes over the liquid solvent, the solvent reacts selectively with the CO2 in the air, pulling the CO2 into the solvent and trapping it. The rest of the substances in the air continue to circulate—without the CO2.

Carbon Removal: Carbon removal is a similar term to carbon storage, and it refers to removing CO2 from the atmosphere through various means. CO2 can be removed and stored underground in reservoirs, but CO2 can also be removed in other ways, such as by planting trees, relying on regenerative agriculture, or cultivating seaweed in oceans—all of which involve absorbing CO2. Carbon removal is also sometimes referred to as carbon dioxide removal (CDR). 

Soil Carbon Sequestration: Soil carbon sequestration is the practice of adapting land-use methods to encourage soil to absorb CO2 from our atmosphere and store it. Also referred to as regenerative agriculture, soil carbon sequestration involves managing land with practices such as low-till or no-till farming, planting cover crops, and applying compost to fields. 

Structural Trapping: Structural trapping is the process of storing CO2 underground within a structural feature that prevents the gas from migrating elsewhere in the rock or escaping. These structural features are natural barriers such as folds or faults in the rock, mud rocks, salt, or other elements. 

Residual Trapping: Residual trapping is the process of trapping supercritical CO2 in porous rock, which prevents the CO2 plume from migrating and ensures greater CO2 storage success. The amount of CO2 that can be trapped depends on the rock’s features, such as its porosity and wettability.

Coal Seams: A coal seam is a band of coal deposits between other layers of rock. Methane and other gases naturally exist within coal seams, either in pores or in fractures. When a coal seam is unmineable, it can be used for carbon storage. Captured CO2 can be injected into a coal seam, where it displaces the existing methane gas. Once injected, the CO2 remains in the seam, whereas the displaced methane can be recovered and supplied to natural gas systems. 

Lifecycle Emissions: Lifecycle emissions are different than the emissions that occur as something is run. Product lifecycle emissions refers to all emissions associated with the production, use, and disposal of a product, from raw material sourcing and manufacturing through to transportation, sale, use, and disposal.

Net Zero Emissions: Net zero emissions, also known as carbon neutrality, refers to ensuring that the CO2 released into our atmosphere is offset by that same amount being removed through carbon capture and storage, carbon removal, or using less carbon-intensive fuel sources. 

Net Negative Emissions: Net negative emissions go a step further than net zero emissions. Net negative emissions refers to removing more CO2 from the atmosphere than is emitted. This can occur through the same tactics—capture and storage, carbon removal, or using less carbon-intensive fuel sources—but to a much greater degree. 

This is part 2 of our series defining common carbon capture and storage terms. Refer back to this page for these definitions, and reference part 1 of our CCS glossary for additional definitions. If you are looking for additional insights into CCS or assistance with CCS-related endeavors, contact us today.